In motor vehicles, typically, there are several cooling subsystems such as engine cooling with an engine coolant circuit with a radiator, a transmission oil cooling circuit, an engine oil cooling circuit, a power steering cooling circuit, as well as others associated with axle oil, hydraulic fluid, air conditioning, etc.
It is known that interconnecting the individual cooling circuits can be beneficial to the overall power train and cabin climate control systems, as demonstrated by the incorporation of in-tank transmission coolers in one of the end tanks, most often the cold tank, of the engine cooling radiator. In this type of system, as the water (or engine coolant) flows through the radiator, it is cooled by the cross air flow. At the same time, transmission oil is fed through the in-tank oil cooler which, in turn, is cooled by the cooled by the water (or engine coolant) from the radiator. This type of system provides improved start-up conditions for the vehicle since the water (or engine coolant) from the radiator helps to warm up the transmission oil. However, the amount of heat transfer achieved by this type of system is limited since the size of the in-tank oil cooler is restricted due to its “in-tank” location. As well, the amount of heat transfer with this type of system is limited because the maximum temperature difference between the two heat exchange fluids, i.e. the transmission oil and water (or engine coolant), is limited based on the inherent characteristics and operating temperatures of these fluids. A further disadvantage with this type of system is that the use of an in-tank oil cooler tends to decrease the overall thermal efficiency of the radiator as it is difficult to achieve equal flow distribution across the heat exchanger due to the non-optimal header tank shape and obstruction of flow by the in-tank oil cooler.
As the power density of engines increases, there are greater demands on heat dissipation, leading to the proliferation of supplemental cooling provided by liquid-to-air heat exchangers mounted in series with liquid-to-liquid heat exchangers. For instance, it is common to provide supplemental cooling by mounting an oil-to-air transmission oil cooler in series and downstream from the in-tank oil cooler described above. In this type of system, the transmission oil leaves the in-tank oil cooler and is fed into an oil-to-air heat exchanger where it is subject to further heat exchange due to the greater temperature difference between the oil and the air, thereby allowing further cooling. However, the addition of series mounted heat exchangers for supplemental cooling tends to put additional strain on the automobile radiator, thereby further reducing its thermal efficiency and making it difficult to meet the needs for additional cooling and/or heating requirements of the vehicle in general.